Method of making a magnetic head for recording reproducing



Oct. 17, 1961 o. KORNEI METHOD OF MAKING A MAGNETIC HEAD FOR RECORDING REPRODUCING Original Filed Oct. 21. 1952 FIG FIG.3B

INVENTOR OTTO KORNEI ATTORNEY .This invention pertains to a transducer head for magnetic recording and reproducing purposes.

This application is a division of my application Serial Number 315,994, filed October 21, 1952, now Patent Number 2,754,569 for Magnetic Head for Recording Reproducing.

An object of this invention is to provide a very small magnetic transducer head which may readily be manufactured in large quantities by mass production techniques to produce heads which are very uniform in quality.

Another object of my invention is to provide a very small magnetic transducer head particularly for use with a motion picture projector wherein the head is adapted to record on or reproduce from a small portion of the width of the film.

Another object of the present invention is to provide a magnetic transducer head which will withstand severe mechanical vibrations and adverse atmospheric conditions.

Still another object of the invention is to provide a new and novel method of manufacturing magnetic transducer heads which produces small, uniform heads at a low cost. v

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

An aspect of the present invention is the method of making a transducer head wherein a ring core of magnetizable material is cut open along a line substantially parallel to the axis of the core to form two planar end faces. Thereafter the core is deformed by compressing it in a direction substantially perpendicular to the planes of the end faces to force the two end faces together with a non-magnetic shim between the two end faces until the two end faces are parallel and are in engagement with the shim. Thereafter the two end faces and the shim are soldered together, and a coil is wound about the core.

In the drawing FIG. 1 is an isometric view of a section of slotted tubing from which the core may be made;

FIG. 2 shows the tubing of FIG. 1 after the spacer has been soldered into the slot;

,FIG.3 is an isometric view of a portion of the tubing of FIG. 2 with an electrical winding around the core;

FIG. 3-A is an end view showing the relative positions of the slot faces of the tubing, and in dotted lines showing an undesirable position of the slot faces of the tubing if they are made t o meet transversely by improperly compressing the tubing;

FIG. 3B isan end view of the tubing showing the desirable position/of the slot faces of the tubing after permanent predeformation in accordance with the invention;

FIG. 4- is an end view of the partially completed head;

FIG. 5 is an end view of the head after the casting material has been added;

FIG. 6 is an end view showing the head after a portion of the housing and the casting material has been ground away to expose the gap region of the core;

FIG. 7 is a top view of the head shown in FIG. 6.

.nited States tent- With reference to the single sheet of drawing there is shown in FIG. 1 a length of tubing 10, of high permeability magnetizable material having a longitudinal slot 11 cut preferably in a plane which includes the axis of the tube to form two planar end faces 12 and 13. After the tube shown in FIG. 1 is prepared a shim 14 of non-magnetizable material such as metal foil is placed in the gap 11, between the two end faces 12, 13, and the tubing is then carefully squeezed shut upon the shim. The thickness of the shim will thus determine the length of the non-magnetic gap in the magnetic core. The end faces 12, 13 are held tightly against the shim 14 and solder 15 is applied along the inner face to solder the two end faces of the tubing to opposite sides of the shim 14 thereby holding shim 14 in place. The tubing which has a preferred diameter of about A of an inch is then carefully cut into short sections, for instance about A of an inch in length, by sawing, grinding, or the like. The length of each of these individual ring shaped sections equals the intended track width of the head. After removing any burrs which may have been caused by the cutting operation, a thin insulating layer is applied to the ring shaped section preferably exempting, however, the regions on either side of the gap. One method of applying the insulation is to dip the lower portion of the core in lacquer which is then caused to harden. Another method is to wrap portions of the core with thin insulating tape. A toroidal winding 16, preferably in a single layer only, is then applied to the core, over the insulating layer, and symmetrically with respect to the gap 23 to form the core assembly shown in FIG. 3.

In the formation of the core assembly it is very important that the deformation of the tubing 10 to close the planar end faces 12, 13 about the shim 14, be done in such a manner that in the finished core assembly the two planar end faces 12, 13 are accurately parallel to each other.

' FIG. 3-A illustrates the undesirable relationship which is obtained between the end faces 12 and 13 if the tubing 10 is improperly deformed. This produces an undesirable inverted V-shaped notch 17, resulting from the end faces 12 and 13 not being in parallel relationship to each other. Such a condition is highly detrimental because it would result in a progressive increase of the gap length when some of the core material is removed in a manufacturing step to be described later, or by natural wear caused by the abrasive nature of the record member. It is important for a magnetic transducer head to have and to maintain during its life a gap as short as possible, since the length of the'gap is an important factor in the resolution and thus in the frequency range of a magnetic recording-reproducing transducer. FIG. 3-B shows the relative position of the two end faces 12 and 13 after the tubing 10 has been correctly predeformed in order to align the two end faces 12 and 13 substantially parallel to each other. The preferred method of predeforming the tubing is to apply force in the direction of and substantially at the location of the arrows '18 until the gap is closed and the tubing material slightly, but permanently, deformed into an oval. The deforming force is then removed allowing the end faces 12, 13 to spring slightly apart into the substantially parallel relationship shown in FIG. 3-B. The shim 14 is then inserted in the gap and the gap closed upon it and soldered as shown in FIG. 3. The substantially parallel relationship of the end faces 12, 13 is thus maintained. Any of the shim material 14 which may extend above the face of the tubing is then removed, the tubing is then cut up into short sections, and the coil 16 is wound on each short section, as explained before.

Another method of preventing the occurrence of the inverted .V-gap is to cut slot 11 by means of a specially shaped tool. This produces confronting faces 12, 13 which converge slightly toward the tube center, by an amount suflicient to compensate for the non-parallelism hich would otherwise arise upon :closing of these forces upon the shim 14.

Experience has shown that it is undesirable to utilize the extreme end portions of the tubing for the construction of magnetic heads. The reason for this lies in the fact that the ends of the tube and the ends of the solder joint are usually slightly less uniform than the center portions because of certain unavoidable limitations in the manufacturing processes. The two extreme end por tions of the tubing shown in FIG. 2, should, therefore, be discarded.

After the subassembly shown in FIG. 3 has been fabricated a substantially cylindrical housing 20, preferably formed of magnetizable material, is provided as illustrated in FIG. 4. The subassembly of FIG. 3 is positioned Within the housing 20, preferably with a thin piece of non-magnetic material 21 such as paper or the like placed between the core and the inner face of the housing 20. A leaf spring 22 is inserted between the core 10 and the housing 20 at a location substantially diametrically opposite the gap 23. Thus, the region of the core 10 adjacent to the gap 23 is in engagement with the spacer 21, and the spacer 21 is held in engagement with the inner face of the housing 20 by means of the spring 22 pushing the core '10 against the spacer 21. The leaf spring 22 thus serves a double purpose: it urges the gap region of the core structure toward the inside wall of the housing as required, and it also secures this position until the core structure is finally locked in place by a subsequent resin casting operation. It should be noted that the positioning of the core within the housing by means of the spring 22 can alsobe used to determine other parameters,'such as the gap being parallel to the axis of the cylindrical housing or the core being located at some predetermined distance from one end of the housing.

Electrical contact is made between the core 10 and the housing 20 by means of a small V-shaped leaf spring 30 which is wedged between the core 10 and the housing 20 or by a drop of electrically conductive paint contacting both the core and the housing. This arrangement permits convenient electrical grounding of housing and core at the same time. The subassembly consisting of the housing and the core is now ready to be filled with hardenable liquid resin. This is done with one end of the housing temporarily closed by a suitable fixture. After the resin has hardened the open ends of the housing are closed by the end plates 27 and 28 which may be soldered, cemented or pressed into place. The end plate 27 has a central opening 29 in which there is secured a hollow mounting stud 35. The ends 25 of the toroidal winding 16 are brought out through this stud.

The cover 28 preferably is a separate member secured to the housing 20, though of course this structure is not essential as the housing 20 and the cover can be a single cup-shaped piece.

In order to make the head operative a small portion of the housing 20 is removed, for instance by grinding or milling it away near the location of the gap 23 in the core 10. By this process, as shown in FIG. 6, a small amount of the hardened casting material is also removed at either side of the gap 23 and so is a very small amount of the core material. This exposes the gap 23 and the .core 10, the ground edges 32 of the housing and the ground face of the hardened casting material in such manner that they form a single smooth surface across which the record material may travel. It is preferable 4 that this single surface be 'arcuate in configuration in order to secure the desirable intimate contact between the record member and the gap 23-, and the center of the arc should lie on a line perpendicular to the tangent to the arcuate curve at the location of the gap 23.

The main reason for the spacer 21 between the core 10 and the housing 20 is to reduce the magnetic shunting effect of the housing on the non-magnetic gap. This shunting effect is greatly reduced because of the increase in distance between the housing and the core portions in immediate vicinity of the gap. Without the spacer 21 there would be objectionable magnetic shunting of the signal flux in the core, both in recording as well as in playback, thus reducing the sensitivity of the head.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. In the method of making a magnetic transducer head, the steps of: providing a ring core of magnetizable material; cutting said core open along a line substantially parallel to the axis of said core to form two planar end faces; placing in said out a non-magnetic shim whose thickness is less than the Width of said .cut; deforming said core by compressing substantially along a diameter substantailly perpendicular to the planes of said end faces to force said two end faces together with said non-magnetic shim between the two end faces until the said two planar end faces are parallel and are in engagement with said shim; aflixing said two end faces and said shim together in the aforesaid position; and winding a coil about said core.

2. The method of making a magnetic transducer head as set forth in claim 1 wherein the plane of said cut includes the axis of said core of magnetizable material.

3. The method of making a magnetic transducer head which comprises the steps of providing a one-piece ring of high permeability material; cutting said ring open along a line substantially parallelto the axis of the ring to provide a one-piece ring having two confronting planar end faces; inserting between said end faces a non-magnetic shim whose thickness is less than the width of said out; compressing said ring substantially perpendicular to the planes of said end faces to force said faces into engagement with the shim; securing saidtwo end faces and the shim in the aforesaid position; and winding a coil about said ring.

References Cited in the file of this patent UNITED STATES PATENTS 1,748,993 Purdy Mar. 4, 1930 1,922,828 Stine Aug. 15, 1933 1,978,235 Summers Oct. 23, 1934 2,469,444 Roys May 10, 1949 2,471,650 Pandolfi May 31, 1949 2,586,532 Granfield Feb. 19, 1952 2,621,259 Grantham Dec. 9, 1952 2,682,021 Elmen June 22, 1954 2,715,659 Ibuka et a1. Aug. 16, 1955 2,736,776 Camras Feb. 28, 1956 2,761,911 Camras 'Sept. 4, 1956 2,822,428 Wood Feb. 4, 1958 2,836,881 Pollock June 3, 1958 FOREIGN PATENTS 661,428 Great Britain Nov. 21, 1951 

